Marconi TF1331 Oscilloscope

[AlanBeckett]

If there's any in the EHT Generator thy're maintaining a very low profile
There are, however, the two 500pF Erie Ceramics. They measure OK, but ......

Alan

[Refugee]

It could be on a supply that feeds from some other place on the chassis.

[AlanBeckett]

Indeed so.

Alan

[Skywave]

I realise that there are many, but have you checked for dry joints in suitable places? Although having said that, and having reviewed what you've written, it does sound as though under the fault condition that there is excessive loading on the 5763 anode cct. - which could, of course, be a reflected excessively high (and intermittent) load on the transformer secondary.
► Thought: have you checked for intermittent shorts on the wiring to the CRT base? The wiring there is cramped & crowded with little clearance between the tags. We've been there before - remember . . . ? ◄

In conclusion, I reckon your best bet is to simply carry on with the rest of the work on this 'scope and make a note of the fault conditions that were manifest, so that you have (at least) some reference point to refer to should the fault re-appear at a later date. And there is a chance that it never will - as suggested by Refugee.

Al.

[AlanBeckett]

Yes Al, that was my first thought, but I couldn't find anything. That's also why I suspected the two Erie Ceramics.

I agree with your suggestion to carry on and keep an eye on it.

Alan

[Refugee]

I was thinking along the lines that a decoupling capacitor drawing a bit of currant could reduce the voltage on a power rail and produce the symptom that you have seen.

[AlanBeckett]

I've captured his Little Brother - see attached - a 2203.
Now I only need his Big Brother, a 2200. Anybody got one stashed in the Attic?

The 1331 is being a bit of a pain at the moment, mainly due to the awful layout. The Y Amplifier Diagram is beautifully symetrical, and you might expect that the layout would be the same. In practice it ain't, by a long way. It's even more odd because there's no shortage of space. I look at it and think 'If I was laying that out it wouldn't be like that'. It's no wonder Tektronix won. As it is I seem to spend at least half the limited time I have groping about wondering where a particular valve is. So I've stopped briefly to construct a Diagram showing where the major (Y Amp) Components are.

I also had a near disaster during the heavy rain a couple of days ago. There was a leak in the Garage roof, but I'm damned if I can locate it. Fortunately it didn't drip on the 'scope, just on some Diagrams I'd left on the Bench. The only problem I could find was a lot of Moss on the Roof, so there may have been a build-up of standing water. Anyway, I've got shot of it, so I'll no doubt find out over the weekend when we're forecast for more heavy rain whether I've fixed it.

The 2203? That's for later.

Alan

       

[pwdrive]

I'll swear your workshop is the Tardis, water leaks in roofs, normally a few feet away than where it comes through, good luck.

Lawrence.

[AlanBeckett]

Yes Lawrence, that's what I figured. The heavy rain is forecast for the early hours now so I fear I won't be watching. I don't think it would have posed a big problem, just taken time to dry out.

Alan

[pwdrive]

"Flat roof" Alan or pitched, felt, tiles ?

Lawrence.